1862.] chapters on fungi. 197 



Rhytisma. 



Perithecium of no regular form, bursting, with a more or less 

 flexuous fissure, into transverse fragments. Asci erect. 



Rhytisma acerinum, Pers. Sycamore Rhytisma. Innate, 

 spots confluent, rugose, bursting by flexuous, labiate fissures, 

 disc pale. — Grev. Sc. Crypt. Fl. t. 118. On leaves of the com- 

 mon Sycamore and Maple. Extremely common. 



Almost every Sycamore-tree appears to be more or less affected 

 with this Fungus, which appears in the form of black spots on 

 the leaves in early autumn, disfiguring them much, and appear- 

 ing to produce a premature dccaj^ and fall of the infected leaves. 

 The plant does not perfect its fructification till the spring of the 

 following year, when the leaves have lain long on the damp 

 ground, and the fissures then open and discharge the sporidia 

 in clouds. The asci are clavate, and the sporidia long and fili- 

 form. 



Suborder 4, Sph.eriacei. 



Perithecia free or immersed in a stroma, or receptacle, opening 

 by a distinct punctiform or short linear aperture. Asci mostly 

 springing from the walls. 



This is a very large and important group of Fungi, and con- 

 tains an immense number of species. Of the genus Sphceria 

 alone two hundred species are described in the ' English Flora,' 

 and at least one hundred more have been added to the list of 

 British species since the publication of that work. 



This group is distinguished by the more or less spherical shape 

 of the perithecia, but the plants vary much in outward appear- 

 ance. I shall take the genus Sphseria as the type, and describe 

 several species of it. 



Sph^ria. 



Perithecia rounded, entire, furnished at the apex with a minute 

 orifice. Asci converging, at length dissolving. 



This extensive genus is now divided into a number of different 

 genera, corresponding (generally) with the principal divisions of 

 it, as given in the * English Flora ;' but as I have taken this 

 as my text-book, I shall not distinguish these new genera. The 

 sporidia of the Sphceria are very various in form, and often very 

 curiously marked and divided. They are beautiful objects under 

 . the microscope. 



